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Member Since 04 Oct 2011
Offline Last Active Today, 01:17 PM

Topics I've Started

My Thoughts On Element Life

07 April 2017 - 11:41 AM

People are always asking about element life, so here are my thoughts on that subject:


On my personal kilns I get 150-160 firings out of my elements, doing a combination of cone 04 bisque and cone 6 glaze, probably 35% bisque and 65% glaze. This is true for both my big 21 cubic foot kiln and my small 4 cubic foot kiln, and is consistent from year to year. Both are L&L kilns with standard elements, not quads. I see similar numbers in my customers' kilns of all brands. I have to change the elements in my small kiln every year, in my big kiln every 2 years.


According to my records I've currently got 241 firings on the thermocouples on my small kiln. I should probably check those soon. They do tend to last longer than the elements, though, because they are thicker and are in protection tubes.


Only firing to low fire temps makes a big difference in element life. Today I did a checkup on an L&L E23T that I installed in a school in 2009. They do about 55 firings a year, all low fire- bisque to 04, glaze to 05. The kiln currently has 418 firings on its original elements, relays and thermocouples. The element resistance is almost perfect. Visually they're starting to show their age, though, and I expect that they'll start to degrade more quickly over the next year. I told them to budget for an element change at the end of the 2017-2018 school year. I wouldn't be surprise if they hit 500 firings.


All of this is subject to what's going on in your specific kiln, though. I have a customer who only gets 70 cone 6 glaze firings out of her elements because she does a really long, slow soak at the high end. She could get 100 with a typical firing schedule. The types of glazes you use, and how you load the kiln will also effect element life. Don't put your pots right up against the kiln walls! I'm also convinced that doing a combination of bisque and cone 6 will get you more cone 6 firings than just firing cone 6 all the time. I have absolutely no science to back that up, but my customers who only use their kiln for cone 6 glaze firings tend to get a slightly fewer firings out of their elements.


Maxing out your kiln will cost you. I have a customer who is using their Skutt 1227, 208 volt single phase kiln for cone 5. On that voltage and phase it is only rated for cone 5, so they are maxing out what the kiln can do, and it's definitely costing them. Once the element resistance changes just a little bit, the kiln can no longer get to cone 5 and we have to change the elements. If the kiln was rated for cone 8 or cone 10, it could handle more resistance change before it struggled to get to cone 5. The customer is supposed to be trying some firings to cone 3 with a hold to get to 5. Hopefully that will work out and help with their element life. In my tests, higher temps seem to burn out elements faster than holds.


Keep your elements clean. Vacuum out the kiln occasionally. Monthly would be fine, but definitely any time something blows up. All the little shards on the elements cause hot spots, which lessen the element life. I worked on a kiln at a school once that was only used for low fire pots. The teacher never vacuumed it out when the kids' work blew up, and the bottom element was full of shards, like really full. As we all know, low fire clay melts when it gets too hot. Well, the clay shards caused enough hot spots that all of the shards melted and fused the entire bottom ring of the element into the bricks. It was just a big tube of glass filling the element grooves. I had to replace all of the bricks in the bottom row. $$$


Have a great weekend!

Long Lasting Vent Ducting

29 November 2016 - 12:53 PM

I've been testing a black thermoplastic vent ducting for more than 2 1/2 years now, and it's held up great. You can get it at McMaster-Carr HERE (link is for 3" but you can get it in any size). It's rated for 250F, so plenty high for kiln venting. I've used it for at least 550 firings and it's still as soft and flexible as the day I installed it, even where it connects down under the kiln. It costs about 4 times more than the aluminum semi-rigid ducting that comes with most vent systems, but it's way more durable and last a lot longer. You can actually step on it without hurting it.

Sponge Holder Pricing

13 September 2016 - 01:39 PM

What do you charge for your sponge holders? I hate making them, but they sell really well. I've been slowly raising my prices this summer, and they're still selling at the same volume, but there has to be a top end. I'm up to $17, but I have a feeling folks won't pay $20 or more. Am I wrong?

Interesting Wheel Pedal Repair

25 August 2016 - 12:46 PM

On Tuesday one of my Thomas Stuart wheels needed repair. The pedal wouldn't respond unless you wiggled the cord. On Wednesday the wheel next to it starting going full speed as soon as you turned on the power switch. It turned out that both needed the same repair, which was not replacement of the pedal guts/potentiometer as I initially thought. Instead, the problem was the cord, specifically right where it goes into the pedal. The plastic cord grip nut at that location puts a lot of pressure on the wires, and over the last 12 years wore them out. I couldn't tell specifically what was happening, but they were clearly fraying or shorting out. Anyway, I simply cut out that section of the cord, spliced the ends of the 4 wires, and hid the splices inside the pedal. The cord is now a few inches shorter, but the wheels are up and running again.

Replacing Kiln Power Cords

12 May 2016 - 11:53 AM

There's often talk here on the forum about replacing power cords on kilns. This may be because the prongs on the cord don't match the outlet, or a longer cord is needed. It seems like a simple thing, but there are a few things you need to look for:


1. If it's a new kiln, replacing the cord on a new kiln may void the warranty unless it's done by an approved technician or with a cord from the manufacturer. True, it would be tough for them to ever find out, but it could happen if you need a tech in the future, and karma can be a real bugger. Plus it's usually easier to replace the wall outlet than change the cord. Also, changing the power cord to one with a different plug configuration or length length may void the UL listing (if the kiln has one), which may affect how your insurance company feels about the kiln. In all cases, you should check with the manufacturer first before making changes.


2. Make sure the new cord is rated for the same amperage as the old cord. Too small and you'll have a major safety issue on your hands.


3. Make sure it has the same number of prongs. Single phase kilns usually have 3 prongs- two hots and a ground. 3 phase kilns have 4 prongs- 3 hots and a ground. Some single phase kilns also have 4 prongs- 2 hots, a neutral and a ground. You cannot change this! Never snap off a grounding prong! It is very dangerous to fire a kiln that is not grounded.


4. Make sure the cord is rated for 105C/220F. This is the one that everyone overlooks. Most power cords you can get at the hardware store are only rated for 90C, which could overheat.


5. Wire it up properly. That means putting the hots, ground and neutral in the right places, as well as using the proper strain relief to hold the cord tight in the control box. Make sure all the connections are good and tight!


6. Building your own cord is often the best way to go, especially if you need a longer than normal cord. SEOOW type cords are wonderfully flexible and easy to work with. They can be purchased online from McMaster Carr or other sellers. You just have to attach the appropriate plug to the cord, which isn't all that difficult. I have found that plugs from McMaster are pretty pricey, so I usually get the plug from Ace, Lowes, etc. If ring terminals are required for the kiln connection, I recommend using high temp terminals. If the old wires have heat resistant sleeves on them, you can reuse them on the new cord if they're in good condition. Otherwise get new sleeves.


Happy wiring!